Why would anyone want class AB amp when class A always sounds better ?

Cost ? Heat? Reliability?

Why would anyone prefer a wife of fifty years, when a Russian model is cuter?

I can answer that one.
I think this will be a fair comparison:

Same system other than the amp. (Speakers are Sonus Faber Seraphino).

I have had a Pass Labs X-250.8 (class AB) for the last year or so.

A couple of moths ago I could try at home a pair of Pass labs XA-60.8 monoblocks. Same manufacturer and not very different price.

I thought that if the X250.8 delivers it’s first 16 watts in class A and it never leaves class A, then I was good to go, Pass class A all the time.

BUT BIAS (current, ampers) of class A in the XA-60.8 are 3 times higher than in X-250.8

Does it matter? Well, I sold my 250 and I couldn’t be happier now with the XA-60.8s

Better timbre, overtones, layers, soundstage …

Same brand, not very different price and for me it makes a hell of a difference.

I’m not trying to argue, just contribute to the community with my recent experience.

Since I speak my truth, I never question another persons truth.  I think that's foolish.  I merely attempt to understand the other person's truth.
Different strokes for different folks. You do you and let people do what they want. It’s called freedom of choice.